The present invention relates generally to radio frequency identification (RFID) antennas, and more specifically, to RFID antennas arranged in arrays.
A RFID system uses radio frequency transmission to identify, categorize, locate and track objects. The RFID system comprises two primary components: a transponder or the RFID tag and a reader. The tag is a device that generates electrical signals or pulses interpreted by the reader. The reader is a transmitter/receiver combination (transceiver) that activates and reads the identification signals from the transponder. The RFID tags are attached to objects that need to be tracked, and can be programmed to broadcast a specific stream of data denoting the object's identity, such as serial and model numbers, price, inventory code and date. A reader will detect the “tagged” object and further connects to a large network that will send information on the objects to interested parties such as retailers and product manufacturers. The RFID tags are considered to be intelligent bar codes that can communicate with a networked system to track every object associated with a designated tag. Therefore, the RFID tags are expected to be widely used in supply chain management, such as tracking shipping and handling. In such supply chain management applications, merchandize are often packed in pallets or large piles of containers. Conventional horn antennas have been used in such supply chain management applications. FIG. 1 shows a horn antenna 110, which is connected with a RFID reader 120, that broadcasts radio frequency (RF) energy toward a pallet 130 packed with RFID tagged merchandise. Due to the nature of the horn antenna 110, the broadcasted RF energy beams out in a large fan-out way. For the large pallet 130, the RF signal strength is not uniform, i.e., not all the RFID tagged items in the pallet 130 may be read. It is certainly not efficient in terms of transmitting and receiving RF signals. Besides, such a horn antenna tends to read any tagged items within a certain range, even those that are outside the pallet 130 and not intended to be read.
In view of the above applications, there is clearly a need to develop a RFID antenna system that facilitates reading 100% of the tagged items in a desired object space, and 0% in undesired spaces. If a pallet is the desired object space, then any space outside of the pallet is the undesired space.